Transmission Diagnosis - With Codes: Description: General

The ZF4HP22 transmission is used on the 4.0L models. The ZF4HP24 transmission is used on the 4.6L models to accommodate the increased power output of the larger engine. Both units are of similar construction, with the ZF4HP24 unit being slightly longer. The operation of both units is the same.

Automatic transmission vehicles are fitted with an "H" gate gear selector mechanism. The gear selector mechanism combines the operation of the transmission gear selector lever and the transfer box high/low gear range selection. Selections on the gear selector lever assembly are transmitted by a selector cable to a gear position switch.

The gear position switch on the transmission passes gear selection signals to an auto gear box control unit located below the left front seat, which outputs the appropriate control signals to an electro-hydraulic valve body in the transmission. A mode switch enables the driver to change the control mode of the auto gear box control unit between manual, economy and sport. The auto gear box control unit provides signals to the message center in the instrument cluster to indicate the control mode and system status.

The automatic transmission features a pressure lubrication system and is cooled by pumping the lubricant through an oil cooler located in front of the engine cooling radiator.

This model is equipped with a revised auto gear box control unit with Controller Area Network (CAN) digital communications between the auto gear box control unit and the ECM.